Studies on Cobalt in Alluvial and Sedentary Soils of Bihar
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Date
1985
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Birsa Agricultural University, Ranchi
Abstract
The cobalt studies were undertaken in 28 surface soil samples (0-20 cm) belonging to thirteen broad Soil Association Groups scattered in different physiographic regions of the State of Bihar, namely young and recent alluvial (calcareous and non-calcareous) areas of north Bihar; old alluvium of south Bihar and sedentary soils of Chotanagpur and Santhal Parganas plateau regions and also varying in mineralogical, physical & chemical properties.
The total content of cobalt in these soils varied from 6.6 to 46.0 ppm with a mean value of 21.7 ppm. Sedentary and alluvial soils of south Bihar are comparatively richer in total Co content as compared to alluvial soils of north Bihar. Almost similar trend was found in respect of total content of Zn, Cu, Fe & n in these soils also. Besides, total Co was found to be significantly and positively correlated with so11 pli (r= 0.445), organic carbon (r=0.544), available (r= 0.496), DTPA-n (r= 0.454), finer fractions i.e. silt+clay % (r= 0.603) and total iron (r = 0.728) indicating pronounced influence of edaphic factors on total Co status of these soils.
Available Co (DTPA-Co) also showed variation from 0.06 to 1.0 ppm with an average value of 0.30 ppm in these soils. Like total Co, available Co also appeared to be higher in sedentary soils and lower in north Bihar alluvial soils. South Bihar soils occupied the intermediate position. Besides, other micronutrients also followed the same trend. Available Co exhibited a highly significant negative correlation (r= -0.609) with soil pH. However it did not bear any relationship with other soil properties.
Cobalt adsorption increased with increasing con centration of added Co but the adsorption isotherms varied in their shapes. The magnitude of Co adsorption was found to be higher in calcareous soil of Pachrukhi containing fairly high amount of clay, manganese and organic carbon and it was the lowest in Pokharvinde non-calcareous soil. Langmuir constant such as adsorption maxima vas found to be significantly and positively correlated with clay (r = 0.913) and DTPA extractable Mn (r= 0.820). pH had also showed a significant positive relationship with bonding energy constant (r=0.790) but not with adsorption maxima.
Buffering capacity in these soils varied from 12.0 to 94.6. It was found to be the highest in Pachrukhi soil and the lowest in Pokharvinde soil. It maintained the same trend as the k and n values of the Freundlich constants. Supply parameter of Co in these soils ranged from 0.69 (Rahua) to 5.28 (Sabour). It was higher in neutral soils and comparatively lower in acidic soils.
The extractability of different reagents with regard to Co extraction from soils followed the descending order as follows:
N/10 HC17 EDTA7 Acetic acid EDTA + NH₂OAC 7 DTPA 7 EDTA + (NH)2CO3
The results also show that EDTA, EDTA+ (NH4)2CO3 and DTPA had shown a significant but negative correlation with soil pH showing the pronounced adverse effect of pH on the extractability of Co in soils.
Sand culture experiment to study the influence of various levels of Co application on growth, nitrogen content, and Co uptake by moong crops indicated that increasing levels of Co had significant effects on dry matter yield, height of plants, nitrogen content and Co uptake by moong crop only upto 6.0 ppm. Drastic reduction in all the above parameters was noticed at 10.0 ppm of Co level showing the detrimental effect of this dose on the growth of the crop. Recovery of added Co decreased from 235 to 55.2% with increasing dose of Co from 1.0 to 10.0 ppm.
Micronutrient studies conducted in soils supporting forage crops exhibited more depletion of available Co from soils leguminous crops (berseen and lucerne) as compared to other forage crops indicating higher requirement and differential behavior of the former than the latter in respect of Co utilization.
Removal pattern of Co by forage crops also showed that the highest Co removal (39.2 g/ha) was found by berseen crop and the lowest (2.2 g/ha) by barley.
Pot experiment to study the influence of line, organic manure and phosphorus on the uptake of Co by crops grown in acid soils indicated significant increase in Co uptake by moong crop due to application of lime, phosphorus and organic manure. However, on maize crop phosphorus application did not show any significant effect on the uptake of Co. Interaction effects of Soil x Lime (S x L), Phosphorus x Line (P x L) and Soil x Organic manure x Lime (S xH x L) came out to be significant.